package parser

import (
	"fmt"
	"regexp"
	"strconv"
	"time"
)

// ErrorEntry holds a parsed nginx error log entry.
type ErrorEntry struct {
	Time    time.Time
	Level   string // debug/info/notice/warn/error/crit/alert/emerg
	PID     int
	TID     int
	ConnID  int // 0 if not present
	Message string
}

// errorLogRe matches nginx error log format.
// Groups: time, level, pid, tid, connID (optional), message
var errorLogRe = regexp.MustCompile(
	`^(\d{4}/\d{2}/\d{2} \d{2}:\d{2}:\d{2}) \[(\w+)\] (\d+)#(\d+): (?:\*(\d+) )?(.+)$`,
)

const errorTimeLayout = "2006/01/02 15:04:05"

// ParseErrorLine parses a single nginx error log line.
// Returns an error for malformed lines.
func ParseErrorLine(line string) (ErrorEntry, error) {
	m := errorLogRe.FindStringSubmatch(line)
	if m == nil {
		return ErrorEntry{}, fmt.Errorf("error: no match: %q", line)
	}

	t, err := time.ParseInLocation(errorTimeLayout, m[1], time.UTC)
	if err != nil {
		return ErrorEntry{}, fmt.Errorf("error: parse time %q: %w", m[1], err)
	}

	pid, err := strconv.Atoi(m[3])
	if err != nil {
		return ErrorEntry{}, fmt.Errorf("error: parse pid %q: %w", m[3], err)
	}

	tid, err := strconv.Atoi(m[4])
	if err != nil {
		return ErrorEntry{}, fmt.Errorf("error: parse tid %q: %w", m[4], err)
	}

	var connID int
	if m[5] != "" {
		connID, err = strconv.Atoi(m[5])
		if err != nil {
			return ErrorEntry{}, fmt.Errorf("error: parse connid %q: %w", m[5], err)
		}
	}

	return ErrorEntry{
		Time:    t,
		Level:   m[2],
		PID:     pid,
		TID:     tid,
		ConnID:  connID,
		Message: m[6],
	}, nil
}